In many integrated circuit designs, it is desirable to be able to configure shallow planar features. Unfortunately, achieving planarization of such features across an entire wafer containing a plurality of such features distributed across the wafer is very difficult. Typically, very tight control of the planarization process is necessary in order to avoid excessive loss of the material in certain areas of the wafer, especially where the wafer itself may have variations of thickness (e.g., due to warping, build-up of structures, etc.)
The ability to configure shallow planar layers across a semiconductor wafer is important in the configuration of thin layers for so-called stacked capacitors useful in memory arrays. One material that is desirable for use in such arrays are transition metal nitrides such as tantalum silicon nitride (TaSiN). TaSiN is especially useful for its oxygen diffusion barrier properties. Processes in current use generally have difficulty in providing a uniform TaSiN surface or require reduced polishing speed.
Thus, there is a need for improve polishing processes which are capable of planarizing shallow configuration materials, especially materials used in the formation of stacked capacitors.
The invention provides methods of improving the polishing uniformity of a material on a substrate. The methods of the invention involve use of a polishing an applied fluid pressure on the backside of the substrate which pressure is changed during the polishing process. The methods are especially useful for polishing thin material layers requiring precise control of polishing across the substrate, e.g., for TaSiN layers used in the formation of gate stacks and stacked capacitors.
In one aspect, the invention encompasses a method of polishing a surface of a substrate by chemical-mechanical polishing, the method comprising:
a) providing a substrate having first surface to be planarized and a second surface on an opposite side of the substrate from the first surface, the first surface having first and second regions,
b) providing a liquid polishing medium,
c) contacting the first surface with the liquid medium and a polishing member, and applying a first pressure against the second surface, and
d) maintaining the contact and applied pressure of step c) while providing movement between the substrate and polishing member, whereby a first portion material of the first surface removed,
e) contacting the first surface with the liquid medium and polishing member, and applying a second pressure against the second surface, and
f) maintaining the contact and applied pressure of step e) while providing movement between the substrate and polishing member, whereby a second portion material of the first surface is removed,
the first and second pressures being sufficiently different from each other whereby a ratio of material removal rate in step (f) in the first region to a material removal rate in step (f) in the second region is different compared to a corresponding material removal rate ratio for the regions in step (d).
The first surface preferably contains at least one transition metal nitride feature, more preferably a tantalum silicon nitride feature. The liquid medium is preferably a slurry containing a particulate abrasive (e.g., an alumina). The slurry is preferably aqueous and preferably also contains an oxidizer, a mineral acid, and hydrogen peroxide.
The method of the invention is especially useful for forming features having a planarized depth of about 1000 xc3x85or less relative to an exposed surface of an adjacent material region of differing composition.
These and other aspects of the invention are described further below.